THREE.GLTFLoader = (function() {
  function GLTFLoader(manager) {
    THREE.Loader.call(this, manager)

    this.dracoLoader = null
    this.ddsLoader = null
    this.ktx2Loader = null
    this.meshoptDecoder = null

    this.pluginCallbacks = []

    this.register(function(parser) {
      return new GLTFMaterialsClearcoatExtension(parser)
    })

    this.register(function(parser) {
      return new GLTFTextureBasisUExtension(parser)
    })

    this.register(function(parser) {
      return new GLTFTextureWebPExtension(parser)
    })

    this.register(function(parser) {
      return new GLTFMaterialsTransmissionExtension(parser)
    })

    this.register(function(parser) {
      return new GLTFLightsExtension(parser)
    })

    this.register(function(parser) {
      return new GLTFMeshoptCompression(parser)
    })
  }

  GLTFLoader.prototype = Object.assign(Object.create(THREE.Loader.prototype), {
    constructor: GLTFLoader,

    load: function(url, onLoad, onProgress, onError) {
      var scope = this

      var resourcePath

      if (this.resourcePath !== '') {
        resourcePath = this.resourcePath
      } else if (this.path !== '') {
        resourcePath = this.path
      } else {
        resourcePath = THREE.LoaderUtils.extractUrlBase(url)
      }

      // Tells the LoadingManager to track an extra item, which resolves after
      // the model is fully loaded. This means the count of items loaded will
      // be incorrect, but ensures manager.onLoad() does not fire early.
      this.manager.itemStart(url)

      var _onError = function(e) {
        if (onError) {
          onError(e)
        } else {
          console.error(e)
        }

        scope.manager.itemError(url)
        scope.manager.itemEnd(url)
      }

      var loader = new THREE.FileLoader(this.manager)

      loader.setPath(this.path)
      loader.setResponseType('arraybuffer')
      loader.setRequestHeader(this.requestHeader)
      loader.setWithCredentials(this.withCredentials)

      loader.load(
        url,
        function(data) {
          try {
            scope.parse(
              data,
              resourcePath,
              function(gltf) {
                onLoad(gltf)

                scope.manager.itemEnd(url)
              },
              _onError
            )
          } catch (e) {
            _onError(e)
          }
        },
        onProgress,
        _onError
      )
    },

    setDRACOLoader: function(dracoLoader) {
      this.dracoLoader = dracoLoader
      return this
    },

    setDDSLoader: function(ddsLoader) {
      this.ddsLoader = ddsLoader
      return this
    },

    setKTX2Loader: function(ktx2Loader) {
      this.ktx2Loader = ktx2Loader
      return this
    },

    setMeshoptDecoder: function(meshoptDecoder) {
      this.meshoptDecoder = meshoptDecoder
      return this
    },

    register: function(callback) {
      if (this.pluginCallbacks.indexOf(callback) === -1) {
        this.pluginCallbacks.push(callback)
      }

      return this
    },

    unregister: function(callback) {
      if (this.pluginCallbacks.indexOf(callback) !== -1) {
        this.pluginCallbacks.splice(this.pluginCallbacks.indexOf(callback), 1)
      }

      return this
    },

    parse: function(data, path, onLoad, onError) {
      var content
      var extensions = {}
      var plugins = {}

      if (typeof data === 'string') {
        content = data
      } else {
        var magic = THREE.LoaderUtils.decodeText(new Uint8Array(data, 0, 4))

        if (magic === BINARY_EXTENSION_HEADER_MAGIC) {
          try {
            extensions[EXTENSIONS.KHR_BINARY_GLTF] = new GLTFBinaryExtension(data)
          } catch (error) {
            if (onError) onError(error)
            return
          }

          content = extensions[EXTENSIONS.KHR_BINARY_GLTF].content
        } else {
          content = THREE.LoaderUtils.decodeText(new Uint8Array(data))
        }
      }

      var json = JSON.parse(content)

      if (json.asset === undefined || json.asset.version[0] < 2) {
        if (onError) onError(new Error('THREE.GLTFLoader: Unsupported asset. glTF versions >=2.0 are supported.'))
        return
      }

      var parser = new GLTFParser(json, {
        path: path || this.resourcePath || '',
        crossOrigin: this.crossOrigin,
        manager: this.manager,
        ktx2Loader: this.ktx2Loader,
        meshoptDecoder: this.meshoptDecoder
      })

      parser.fileLoader.setRequestHeader(this.requestHeader)

      for (var i = 0; i < this.pluginCallbacks.length; i++) {
        var plugin = this.pluginCallbacks[i](parser)
        plugins[plugin.name] = plugin

        // Workaround to avoid determining as unknown extension
        // in addUnknownExtensionsToUserData().
        // Remove this workaround if we move all the existing
        // extension handlers to plugin system
        extensions[plugin.name] = true
      }

      if (json.extensionsUsed) {
        for (var i = 0; i < json.extensionsUsed.length; ++i) {
          var extensionName = json.extensionsUsed[i]
          var extensionsRequired = json.extensionsRequired || []

          switch (extensionName) {
            case EXTENSIONS.KHR_MATERIALS_UNLIT:
              extensions[extensionName] = new GLTFMaterialsUnlitExtension()
              break

            case EXTENSIONS.KHR_MATERIALS_PBR_SPECULAR_GLOSSINESS:
              extensions[extensionName] = new GLTFMaterialsPbrSpecularGlossinessExtension()
              break

            case EXTENSIONS.KHR_DRACO_MESH_COMPRESSION:
              extensions[extensionName] = new GLTFDracoMeshCompressionExtension(json, this.dracoLoader)
              break

            case EXTENSIONS.MSFT_TEXTURE_DDS:
              extensions[extensionName] = new GLTFTextureDDSExtension(this.ddsLoader)
              break

            case EXTENSIONS.KHR_TEXTURE_TRANSFORM:
              extensions[extensionName] = new GLTFTextureTransformExtension()
              break

            case EXTENSIONS.KHR_MESH_QUANTIZATION:
              extensions[extensionName] = new GLTFMeshQuantizationExtension()
              break

            default:
              if (extensionsRequired.indexOf(extensionName) >= 0 && plugins[extensionName] === undefined) {
                console.warn('THREE.GLTFLoader: Unknown extension "' + extensionName + '".')
              }
          }
        }
      }

      parser.setExtensions(extensions)
      parser.setPlugins(plugins)
      parser.parse(onLoad, onError)
    }
  })

  /* GLTFREGISTRY */

  function GLTFRegistry() {
    var objects = {}

    return {
      get: function(key) {
        return objects[key]
      },

      add: function(key, object) {
        objects[key] = object
      },

      remove: function(key) {
        delete objects[key]
      },

      removeAll: function() {
        objects = {}
      }
    }
  }

  /*********************************/
  /********** EXTENSIONS ***********/
  /*********************************/

  var EXTENSIONS = {
    KHR_BINARY_GLTF: 'KHR_binary_glTF',
    KHR_DRACO_MESH_COMPRESSION: 'KHR_draco_mesh_compression',
    KHR_LIGHTS_PUNCTUAL: 'KHR_lights_punctual',
    KHR_MATERIALS_CLEARCOAT: 'KHR_materials_clearcoat',
    KHR_MATERIALS_PBR_SPECULAR_GLOSSINESS: 'KHR_materials_pbrSpecularGlossiness',
    KHR_MATERIALS_TRANSMISSION: 'KHR_materials_transmission',
    KHR_MATERIALS_UNLIT: 'KHR_materials_unlit',
    KHR_TEXTURE_BASISU: 'KHR_texture_basisu',
    KHR_TEXTURE_TRANSFORM: 'KHR_texture_transform',
    KHR_MESH_QUANTIZATION: 'KHR_mesh_quantization',
    EXT_TEXTURE_WEBP: 'EXT_texture_webp',
    EXT_MESHOPT_COMPRESSION: 'EXT_meshopt_compression',
    MSFT_TEXTURE_DDS: 'MSFT_texture_dds'
  }

  /**
   * DDS Texture Extension
   *
   * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Vendor/MSFT_texture_dds
   *
   */
  function GLTFTextureDDSExtension(ddsLoader) {
    if (!ddsLoader) {
      throw new Error('THREE.GLTFLoader: Attempting to load .dds texture without importing THREE.DDSLoader')
    }

    this.name = EXTENSIONS.MSFT_TEXTURE_DDS
    this.ddsLoader = ddsLoader
  }

  /**
   * Punctual Lights Extension
   *
   * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_lights_punctual
   */
  function GLTFLightsExtension(parser) {
    this.parser = parser
    this.name = EXTENSIONS.KHR_LIGHTS_PUNCTUAL

    // Object3D instance caches
    this.cache = { refs: {}, uses: {} }
  }

  GLTFLightsExtension.prototype._markDefs = function() {
    var parser = this.parser
    var nodeDefs = this.parser.json.nodes || []

    for (var nodeIndex = 0, nodeLength = nodeDefs.length; nodeIndex < nodeLength; nodeIndex++) {
      var nodeDef = nodeDefs[nodeIndex]

      if (nodeDef.extensions && nodeDef.extensions[this.name] && nodeDef.extensions[this.name].light !== undefined) {
        parser._addNodeRef(this.cache, nodeDef.extensions[this.name].light)
      }
    }
  }

  GLTFLightsExtension.prototype._loadLight = function(lightIndex) {
    var parser = this.parser
    var cacheKey = 'light:' + lightIndex
    var dependency = parser.cache.get(cacheKey)

    if (dependency) return dependency

    var json = parser.json
    var extensions = (json.extensions && json.extensions[this.name]) || {}
    var lightDefs = extensions.lights || []
    var lightDef = lightDefs[lightIndex]
    var lightNode

    var color = new THREE.Color(0xffffff)

    if (lightDef.color !== undefined) color.fromArray(lightDef.color)

    var range = lightDef.range !== undefined ? lightDef.range : 0

    switch (lightDef.type) {
      case 'directional':
        lightNode = new THREE.DirectionalLight(color)
        lightNode.target.position.set(0, 0, -1)
        lightNode.add(lightNode.target)
        break

      case 'point':
        lightNode = new THREE.PointLight(color)
        lightNode.distance = range
        break

      case 'spot':
        lightNode = new THREE.SpotLight(color)
        lightNode.distance = range
        // Handle spotlight properties.
        lightDef.spot = lightDef.spot || {}
        lightDef.spot.innerConeAngle = lightDef.spot.innerConeAngle !== undefined ? lightDef.spot.innerConeAngle : 0
        lightDef.spot.outerConeAngle = lightDef.spot.outerConeAngle !== undefined ? lightDef.spot.outerConeAngle : Math.PI / 4.0
        lightNode.angle = lightDef.spot.outerConeAngle
        lightNode.penumbra = 1.0 - lightDef.spot.innerConeAngle / lightDef.spot.outerConeAngle
        lightNode.target.position.set(0, 0, -1)
        lightNode.add(lightNode.target)
        break

      default:
        throw new Error('THREE.GLTFLoader: Unexpected light type, "' + lightDef.type + '".')
    }

    // Some lights (e.g. spot) default to a position other than the origin. Reset the position
    // here, because node-level parsing will only override position if explicitly specified.
    lightNode.position.set(0, 0, 0)

    lightNode.decay = 2

    if (lightDef.intensity !== undefined) lightNode.intensity = lightDef.intensity

    lightNode.name = parser.createUniqueName(lightDef.name || 'light_' + lightIndex)

    dependency = Promise.resolve(lightNode)

    parser.cache.add(cacheKey, dependency)

    return dependency
  }

  GLTFLightsExtension.prototype.createNodeAttachment = function(nodeIndex) {
    var self = this
    var parser = this.parser
    var json = parser.json
    var nodeDef = json.nodes[nodeIndex]
    var lightDef = (nodeDef.extensions && nodeDef.extensions[this.name]) || {}
    var lightIndex = lightDef.light

    if (lightIndex === undefined) return null

    return this._loadLight(lightIndex).then(function(light) {
      return parser._getNodeRef(self.cache, lightIndex, light)
    })
  }

  /**
   * Unlit Materials Extension
   *
   * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_unlit
   */
  function GLTFMaterialsUnlitExtension() {
    this.name = EXTENSIONS.KHR_MATERIALS_UNLIT
  }

  GLTFMaterialsUnlitExtension.prototype.getMaterialType = function() {
    return THREE.MeshBasicMaterial
  }

  GLTFMaterialsUnlitExtension.prototype.extendParams = function(materialParams, materialDef, parser) {
    var pending = []

    materialParams.color = new THREE.Color(1.0, 1.0, 1.0)
    materialParams.opacity = 1.0

    var metallicRoughness = materialDef.pbrMetallicRoughness

    if (metallicRoughness) {
      if (Array.isArray(metallicRoughness.baseColorFactor)) {
        var array = metallicRoughness.baseColorFactor

        materialParams.color.fromArray(array)
        materialParams.opacity = array[3]
      }

      if (metallicRoughness.baseColorTexture !== undefined) {
        pending.push(parser.assignTexture(materialParams, 'map', metallicRoughness.baseColorTexture))
      }
    }

    return Promise.all(pending)
  }

  /**
   * Clearcoat Materials Extension
   *
   * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_clearcoat
   */
  function GLTFMaterialsClearcoatExtension(parser) {
    this.parser = parser
    this.name = EXTENSIONS.KHR_MATERIALS_CLEARCOAT
  }

  GLTFMaterialsClearcoatExtension.prototype.getMaterialType = function(materialIndex) {
    var parser = this.parser
    var materialDef = parser.json.materials[materialIndex]

    if (!materialDef.extensions || !materialDef.extensions[this.name]) return null

    return THREE.MeshPhysicalMaterial
  }

  GLTFMaterialsClearcoatExtension.prototype.extendMaterialParams = function(materialIndex, materialParams) {
    var parser = this.parser
    var materialDef = parser.json.materials[materialIndex]

    if (!materialDef.extensions || !materialDef.extensions[this.name]) {
      return Promise.resolve()
    }

    var pending = []

    var extension = materialDef.extensions[this.name]

    if (extension.clearcoatFactor !== undefined) {
      materialParams.clearcoat = extension.clearcoatFactor
    }

    if (extension.clearcoatTexture !== undefined) {
      pending.push(parser.assignTexture(materialParams, 'clearcoatMap', extension.clearcoatTexture))
    }

    if (extension.clearcoatRoughnessFactor !== undefined) {
      materialParams.clearcoatRoughness = extension.clearcoatRoughnessFactor
    }

    if (extension.clearcoatRoughnessTexture !== undefined) {
      pending.push(parser.assignTexture(materialParams, 'clearcoatRoughnessMap', extension.clearcoatRoughnessTexture))
    }

    if (extension.clearcoatNormalTexture !== undefined) {
      pending.push(parser.assignTexture(materialParams, 'clearcoatNormalMap', extension.clearcoatNormalTexture))

      if (extension.clearcoatNormalTexture.scale !== undefined) {
        var scale = extension.clearcoatNormalTexture.scale

        materialParams.clearcoatNormalScale = new THREE.Vector2(scale, scale)
      }
    }

    return Promise.all(pending)
  }

  /**
   * Transmission Materials Extension
   *
   * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_transmission
   * Draft: https://github.com/KhronosGroup/glTF/pull/1698
   */
  function GLTFMaterialsTransmissionExtension(parser) {
    this.parser = parser
    this.name = EXTENSIONS.KHR_MATERIALS_TRANSMISSION
  }

  GLTFMaterialsTransmissionExtension.prototype.getMaterialType = function(materialIndex) {
    var parser = this.parser
    var materialDef = parser.json.materials[materialIndex]

    if (!materialDef.extensions || !materialDef.extensions[this.name]) return null

    return THREE.MeshPhysicalMaterial
  }

  GLTFMaterialsTransmissionExtension.prototype.extendMaterialParams = function(materialIndex, materialParams) {
    var parser = this.parser
    var materialDef = parser.json.materials[materialIndex]

    if (!materialDef.extensions || !materialDef.extensions[this.name]) {
      return Promise.resolve()
    }

    var pending = []

    var extension = materialDef.extensions[this.name]

    if (extension.transmissionFactor !== undefined) {
      materialParams.transmission = extension.transmissionFactor
    }

    if (extension.transmissionTexture !== undefined) {
      pending.push(parser.assignTexture(materialParams, 'transmissionMap', extension.transmissionTexture))
    }

    return Promise.all(pending)
  }

  /**
   * BasisU Texture Extension
   *
   * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_texture_basisu
   */
  function GLTFTextureBasisUExtension(parser) {
    this.parser = parser
    this.name = EXTENSIONS.KHR_TEXTURE_BASISU
  }

  GLTFTextureBasisUExtension.prototype.loadTexture = function(textureIndex) {
    var parser = this.parser
    var json = parser.json

    var textureDef = json.textures[textureIndex]

    if (!textureDef.extensions || !textureDef.extensions[this.name]) {
      return null
    }

    var extension = textureDef.extensions[this.name]
    var source = json.images[extension.source]
    var loader = parser.options.ktx2Loader

    if (!loader) {
      if (json.extensionsRequired && json.extensionsRequired.indexOf(this.name) >= 0) {
        throw new Error('THREE.GLTFLoader: setKTX2Loader must be called before loading KTX2 textures')
      } else {
        // Assumes that the extension is optional and that a fallback texture is present
        return null
      }
    }

    return parser.loadTextureImage(textureIndex, source, loader)
  }

  /**
   * WebP Texture Extension
   *
   * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Vendor/EXT_texture_webp
   */
  function GLTFTextureWebPExtension(parser) {
    this.parser = parser
    this.name = EXTENSIONS.EXT_TEXTURE_WEBP
    this.isSupported = null
  }

  GLTFTextureWebPExtension.prototype.loadTexture = function(textureIndex) {
    var name = this.name
    var parser = this.parser
    var json = parser.json

    var textureDef = json.textures[textureIndex]

    if (!textureDef.extensions || !textureDef.extensions[name]) {
      return null
    }

    var extension = textureDef.extensions[name]
    var source = json.images[extension.source]
    var loader = source.uri ? parser.options.manager.getHandler(source.uri) : parser.textureLoader

    return this.detectSupport().then(function(isSupported) {
      if (isSupported) return parser.loadTextureImage(textureIndex, source, loader)

      if (json.extensionsRequired && json.extensionsRequired.indexOf(name) >= 0) {
        throw new Error('THREE.GLTFLoader: WebP required by asset but unsupported.')
      }

      // Fall back to PNG or JPEG.
      return parser.loadTexture(textureIndex)
    })
  }

  GLTFTextureWebPExtension.prototype.detectSupport = function() {
    if (!this.isSupported) {
      this.isSupported = new Promise(function(resolve) {
        var image = new Image()

        // Lossy test image. Support for lossy images doesn't guarantee support for all
        // WebP images, unfortunately.
        image.src = ''

        image.onload = image.onerror = function() {
          resolve(image.height === 1)
        }
      })
    }

    return this.isSupported
  }

  /**
   * meshopt BufferView Compression Extension
   *
   * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Vendor/EXT_meshopt_compression
   */
  function GLTFMeshoptCompression(parser) {
    this.name = EXTENSIONS.EXT_MESHOPT_COMPRESSION
    this.parser = parser
  }

  GLTFMeshoptCompression.prototype.loadBufferView = function(index) {
    var json = this.parser.json
    var bufferView = json.bufferViews[index]

    if (bufferView.extensions && bufferView.extensions[this.name]) {
      var extensionDef = bufferView.extensions[this.name]

      var buffer = this.parser.getDependency('buffer', extensionDef.buffer)
      var decoder = this.parser.options.meshoptDecoder

      if (!decoder || !decoder.supported) {
        if (json.extensionsRequired && json.extensionsRequired.indexOf(this.name) >= 0) {
          throw new Error('THREE.GLTFLoader: setMeshoptDecoder must be called before loading compressed files')
        } else {
          // Assumes that the extension is optional and that fallback buffer data is present
          return null
        }
      }

      return Promise.all([buffer, decoder.ready]).then(function(res) {
        var byteOffset = extensionDef.byteOffset || 0
        var byteLength = extensionDef.byteLength || 0

        var count = extensionDef.count
        var stride = extensionDef.byteStride

        var result = new ArrayBuffer(count * stride)
        var source = new Uint8Array(res[0], byteOffset, byteLength)

        decoder.decodeGltfBuffer(new Uint8Array(result), count, stride, source, extensionDef.mode, extensionDef.filter)
        return result
      })
    } else {
      return null
    }
  }

  /* BINARY EXTENSION */
  var BINARY_EXTENSION_HEADER_MAGIC = 'glTF'
  var BINARY_EXTENSION_HEADER_LENGTH = 12
  var BINARY_EXTENSION_CHUNK_TYPES = { JSON: 0x4e4f534a, BIN: 0x004e4942 }

  function GLTFBinaryExtension(data) {
    this.name = EXTENSIONS.KHR_BINARY_GLTF
    this.content = null
    this.body = null

    var headerView = new DataView(data, 0, BINARY_EXTENSION_HEADER_LENGTH)

    this.header = {
      magic: THREE.LoaderUtils.decodeText(new Uint8Array(data.slice(0, 4))),
      version: headerView.getUint32(4, true),
      length: headerView.getUint32(8, true)
    }

    if (this.header.magic !== BINARY_EXTENSION_HEADER_MAGIC) {
      throw new Error('THREE.GLTFLoader: Unsupported glTF-Binary header.')
    } else if (this.header.version < 2.0) {
      throw new Error('THREE.GLTFLoader: Legacy binary file detected.')
    }

    var chunkView = new DataView(data, BINARY_EXTENSION_HEADER_LENGTH)
    var chunkIndex = 0

    while (chunkIndex < chunkView.byteLength) {
      var chunkLength = chunkView.getUint32(chunkIndex, true)
      chunkIndex += 4

      var chunkType = chunkView.getUint32(chunkIndex, true)
      chunkIndex += 4

      if (chunkType === BINARY_EXTENSION_CHUNK_TYPES.JSON) {
        var contentArray = new Uint8Array(data, BINARY_EXTENSION_HEADER_LENGTH + chunkIndex, chunkLength)
        this.content = THREE.LoaderUtils.decodeText(contentArray)
      } else if (chunkType === BINARY_EXTENSION_CHUNK_TYPES.BIN) {
        var byteOffset = BINARY_EXTENSION_HEADER_LENGTH + chunkIndex
        this.body = data.slice(byteOffset, byteOffset + chunkLength)
      }

      // Clients must ignore chunks with unknown types.

      chunkIndex += chunkLength
    }

    if (this.content === null) {
      throw new Error('THREE.GLTFLoader: JSON content not found.')
    }
  }

  /**
   * DRACO Mesh Compression Extension
   *
   * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_draco_mesh_compression
   */
  function GLTFDracoMeshCompressionExtension(json, dracoLoader) {
    if (!dracoLoader) {
      throw new Error('THREE.GLTFLoader: No DRACOLoader instance provided.')
    }

    this.name = EXTENSIONS.KHR_DRACO_MESH_COMPRESSION
    this.json = json
    this.dracoLoader = dracoLoader
    this.dracoLoader.preload()
  }

  GLTFDracoMeshCompressionExtension.prototype.decodePrimitive = function(primitive, parser) {
    var json = this.json
    var dracoLoader = this.dracoLoader
    var bufferViewIndex = primitive.extensions[this.name].bufferView
    var gltfAttributeMap = primitive.extensions[this.name].attributes
    var threeAttributeMap = {}
    var attributeNormalizedMap = {}
    var attributeTypeMap = {}

    for (var attributeName in gltfAttributeMap) {
      var threeAttributeName = ATTRIBUTES[attributeName] || attributeName.toLowerCase()

      threeAttributeMap[threeAttributeName] = gltfAttributeMap[attributeName]
    }

    for (attributeName in primitive.attributes) {
      var threeAttributeName = ATTRIBUTES[attributeName] || attributeName.toLowerCase()

      if (gltfAttributeMap[attributeName] !== undefined) {
        var accessorDef = json.accessors[primitive.attributes[attributeName]]
        var componentType = WEBGL_COMPONENT_TYPES[accessorDef.componentType]

        attributeTypeMap[threeAttributeName] = componentType
        attributeNormalizedMap[threeAttributeName] = accessorDef.normalized === true
      }
    }

    return parser.getDependency('bufferView', bufferViewIndex).then(function(bufferView) {
      return new Promise(function(resolve) {
        dracoLoader.decodeDracoFile(
          bufferView,
          function(geometry) {
            for (var attributeName in geometry.attributes) {
              var attribute = geometry.attributes[attributeName]
              var normalized = attributeNormalizedMap[attributeName]

              if (normalized !== undefined) attribute.normalized = normalized
            }

            resolve(geometry)
          },
          threeAttributeMap,
          attributeTypeMap
        )
      })
    })
  }

  /**
   * Texture Transform Extension
   *
   * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_texture_transform
   */
  function GLTFTextureTransformExtension() {
    this.name = EXTENSIONS.KHR_TEXTURE_TRANSFORM
  }

  GLTFTextureTransformExtension.prototype.extendTexture = function(texture, transform) {
    texture = texture.clone()

    if (transform.offset !== undefined) {
      texture.offset.fromArray(transform.offset)
    }

    if (transform.rotation !== undefined) {
      texture.rotation = transform.rotation
    }

    if (transform.scale !== undefined) {
      texture.repeat.fromArray(transform.scale)
    }

    if (transform.texCoord !== undefined) {
      console.warn('THREE.GLTFLoader: Custom UV sets in "' + this.name + '" extension not yet supported.')
    }

    texture.needsUpdate = true

    return texture
  }

  /**
   * Specular-Glossiness Extension
   *
   * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_pbrSpecularGlossiness
   */

  /**
   * A sub class of THREE.StandardMaterial with some of the functionality
   * changed via the `onBeforeCompile` callback
   * @pailhead
   */

  function GLTFMeshStandardSGMaterial(params) {
    THREE.MeshStandardMaterial.call(this)

    this.isGLTFSpecularGlossinessMaterial = true

    //various chunks that need replacing
    var specularMapParsFragmentChunk = ['#ifdef USE_SPECULARMAP', '	uniform sampler2D specularMap;', '#endif'].join('\n')

    var glossinessMapParsFragmentChunk = ['#ifdef USE_GLOSSINESSMAP', '	uniform sampler2D glossinessMap;', '#endif'].join('\n')

    var specularMapFragmentChunk = [
      'vec3 specularFactor = specular;',
      '#ifdef USE_SPECULARMAP',
      '	vec4 texelSpecular = texture2D( specularMap, vUv );',
      '	texelSpecular = sRGBToLinear( texelSpecular );',
      '	// reads channel RGB, compatible with a glTF Specular-Glossiness (RGBA) texture',
      '	specularFactor *= texelSpecular.rgb;',
      '#endif'
    ].join('\n')

    var glossinessMapFragmentChunk = [
      'float glossinessFactor = glossiness;',
      '#ifdef USE_GLOSSINESSMAP',
      '	vec4 texelGlossiness = texture2D( glossinessMap, vUv );',
      '	// reads channel A, compatible with a glTF Specular-Glossiness (RGBA) texture',
      '	glossinessFactor *= texelGlossiness.a;',
      '#endif'
    ].join('\n')

    var lightPhysicalFragmentChunk = [
      'PhysicalMaterial material;',
      'material.diffuseColor = diffuseColor.rgb * ( 1. - max( specularFactor.r, max( specularFactor.g, specularFactor.b ) ) );',
      'vec3 dxy = max( abs( dFdx( geometryNormal ) ), abs( dFdy( geometryNormal ) ) );',
      'float geometryRoughness = max( max( dxy.x, dxy.y ), dxy.z );',
      'material.specularRoughness = max( 1.0 - glossinessFactor, 0.0525 ); // 0.0525 corresponds to the base mip of a 256 cubemap.',
      'material.specularRoughness += geometryRoughness;',
      'material.specularRoughness = min( material.specularRoughness, 1.0 );',
      'material.specularColor = specularFactor;'
    ].join('\n')

    var uniforms = {
      specular: { value: new THREE.Color().setHex(0xffffff) },
      glossiness: { value: 1 },
      specularMap: { value: null },
      glossinessMap: { value: null }
    }

    this._extraUniforms = uniforms

    this.onBeforeCompile = function(shader) {
      for (var uniformName in uniforms) {
        shader.uniforms[uniformName] = uniforms[uniformName]
      }

      shader.fragmentShader = shader.fragmentShader
        .replace('uniform float roughness;', 'uniform vec3 specular;')
        .replace('uniform float metalness;', 'uniform float glossiness;')
        .replace('#include <roughnessmap_pars_fragment>', specularMapParsFragmentChunk)
        .replace('#include <metalnessmap_pars_fragment>', glossinessMapParsFragmentChunk)
        .replace('#include <roughnessmap_fragment>', specularMapFragmentChunk)
        .replace('#include <metalnessmap_fragment>', glossinessMapFragmentChunk)
        .replace('#include <lights_physical_fragment>', lightPhysicalFragmentChunk)
    }

    Object.defineProperties(this, {
      specular: {
        get: function() {
          return uniforms.specular.value
        },
        set: function(v) {
          uniforms.specular.value = v
        }
      },

      specularMap: {
        get: function() {
          return uniforms.specularMap.value
        },
        set: function(v) {
          uniforms.specularMap.value = v

          if (v) {
            this.defines.USE_SPECULARMAP = '' // USE_UV is set by the renderer for specular maps
          } else {
            delete this.defines.USE_SPECULARMAP
          }
        }
      },

      glossiness: {
        get: function() {
          return uniforms.glossiness.value
        },
        set: function(v) {
          uniforms.glossiness.value = v
        }
      },

      glossinessMap: {
        get: function() {
          return uniforms.glossinessMap.value
        },
        set: function(v) {
          uniforms.glossinessMap.value = v

          if (v) {
            this.defines.USE_GLOSSINESSMAP = ''
            this.defines.USE_UV = ''
          } else {
            delete this.defines.USE_GLOSSINESSMAP
            delete this.defines.USE_UV
          }
        }
      }
    })

    delete this.metalness
    delete this.roughness
    delete this.metalnessMap
    delete this.roughnessMap

    this.setValues(params)
  }

  GLTFMeshStandardSGMaterial.prototype = Object.create(THREE.MeshStandardMaterial.prototype)
  GLTFMeshStandardSGMaterial.prototype.constructor = GLTFMeshStandardSGMaterial

  GLTFMeshStandardSGMaterial.prototype.copy = function(source) {
    THREE.MeshStandardMaterial.prototype.copy.call(this, source)
    this.specularMap = source.specularMap
    this.specular.copy(source.specular)
    this.glossinessMap = source.glossinessMap
    this.glossiness = source.glossiness
    delete this.metalness
    delete this.roughness
    delete this.metalnessMap
    delete this.roughnessMap
    return this
  }

  function GLTFMaterialsPbrSpecularGlossinessExtension() {
    return {
      name: EXTENSIONS.KHR_MATERIALS_PBR_SPECULAR_GLOSSINESS,

      specularGlossinessParams: [
        'color',
        'map',
        'lightMap',
        'lightMapIntensity',
        'aoMap',
        'aoMapIntensity',
        'emissive',
        'emissiveIntensity',
        'emissiveMap',
        'bumpMap',
        'bumpScale',
        'normalMap',
        'normalMapType',
        'displacementMap',
        'displacementScale',
        'displacementBias',
        'specularMap',
        'specular',
        'glossinessMap',
        'glossiness',
        'alphaMap',
        'envMap',
        'envMapIntensity',
        'refractionRatio'
      ],

      getMaterialType: function() {
        return GLTFMeshStandardSGMaterial
      },

      extendParams: function(materialParams, materialDef, parser) {
        var pbrSpecularGlossiness = materialDef.extensions[this.name]

        materialParams.color = new THREE.Color(1.0, 1.0, 1.0)
        materialParams.opacity = 1.0

        var pending = []

        if (Array.isArray(pbrSpecularGlossiness.diffuseFactor)) {
          var array = pbrSpecularGlossiness.diffuseFactor

          materialParams.color.fromArray(array)
          materialParams.opacity = array[3]
        }

        if (pbrSpecularGlossiness.diffuseTexture !== undefined) {
          pending.push(parser.assignTexture(materialParams, 'map', pbrSpecularGlossiness.diffuseTexture))
        }

        materialParams.emissive = new THREE.Color(0.0, 0.0, 0.0)
        materialParams.glossiness = pbrSpecularGlossiness.glossinessFactor !== undefined ? pbrSpecularGlossiness.glossinessFactor : 1.0
        materialParams.specular = new THREE.Color(1.0, 1.0, 1.0)

        if (Array.isArray(pbrSpecularGlossiness.specularFactor)) {
          materialParams.specular.fromArray(pbrSpecularGlossiness.specularFactor)
        }

        if (pbrSpecularGlossiness.specularGlossinessTexture !== undefined) {
          var specGlossMapDef = pbrSpecularGlossiness.specularGlossinessTexture
          pending.push(parser.assignTexture(materialParams, 'glossinessMap', specGlossMapDef))
          pending.push(parser.assignTexture(materialParams, 'specularMap', specGlossMapDef))
        }

        return Promise.all(pending)
      },

      createMaterial: function(materialParams) {
        var material = new GLTFMeshStandardSGMaterial(materialParams)
        material.fog = true

        material.color = materialParams.color

        material.map = materialParams.map === undefined ? null : materialParams.map

        material.lightMap = null
        material.lightMapIntensity = 1.0

        material.aoMap = materialParams.aoMap === undefined ? null : materialParams.aoMap
        material.aoMapIntensity = 1.0

        material.emissive = materialParams.emissive
        material.emissiveIntensity = 1.0
        material.emissiveMap = materialParams.emissiveMap === undefined ? null : materialParams.emissiveMap

        material.bumpMap = materialParams.bumpMap === undefined ? null : materialParams.bumpMap
        material.bumpScale = 1

        material.normalMap = materialParams.normalMap === undefined ? null : materialParams.normalMap
        material.normalMapType = THREE.TangentSpaceNormalMap

        if (materialParams.normalScale) material.normalScale = materialParams.normalScale

        material.displacementMap = null
        material.displacementScale = 1
        material.displacementBias = 0

        material.specularMap = materialParams.specularMap === undefined ? null : materialParams.specularMap
        material.specular = materialParams.specular

        material.glossinessMap = materialParams.glossinessMap === undefined ? null : materialParams.glossinessMap
        material.glossiness = materialParams.glossiness

        material.alphaMap = null

        material.envMap = materialParams.envMap === undefined ? null : materialParams.envMap
        material.envMapIntensity = 1.0

        material.refractionRatio = 0.98

        return material
      }
    }
  }

  /**
   * Mesh Quantization Extension
   *
   * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_mesh_quantization
   */
  function GLTFMeshQuantizationExtension() {
    this.name = EXTENSIONS.KHR_MESH_QUANTIZATION
  }

  /*********************************/
  /********** INTERPOLATION ********/
  /*********************************/

  // Spline Interpolation
  // Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#appendix-c-spline-interpolation
  function GLTFCubicSplineInterpolant(parameterPositions, sampleValues, sampleSize, resultBuffer) {
    THREE.Interpolant.call(this, parameterPositions, sampleValues, sampleSize, resultBuffer)
  }

  GLTFCubicSplineInterpolant.prototype = Object.create(THREE.Interpolant.prototype)
  GLTFCubicSplineInterpolant.prototype.constructor = GLTFCubicSplineInterpolant

  GLTFCubicSplineInterpolant.prototype.copySampleValue_ = function(index) {
    // Copies a sample value to the result buffer. See description of glTF
    // CUBICSPLINE values layout in interpolate_() function below.

    var result = this.resultBuffer,
      values = this.sampleValues,
      valueSize = this.valueSize,
      offset = index * valueSize * 3 + valueSize

    for (var i = 0; i !== valueSize; i++) {
      result[i] = values[offset + i]
    }

    return result
  }

  GLTFCubicSplineInterpolant.prototype.beforeStart_ = GLTFCubicSplineInterpolant.prototype.copySampleValue_

  GLTFCubicSplineInterpolant.prototype.afterEnd_ = GLTFCubicSplineInterpolant.prototype.copySampleValue_

  GLTFCubicSplineInterpolant.prototype.interpolate_ = function(i1, t0, t, t1) {
    var result = this.resultBuffer
    var values = this.sampleValues
    var stride = this.valueSize

    var stride2 = stride * 2
    var stride3 = stride * 3

    var td = t1 - t0

    var p = (t - t0) / td
    var pp = p * p
    var ppp = pp * p

    var offset1 = i1 * stride3
    var offset0 = offset1 - stride3

    var s2 = -2 * ppp + 3 * pp
    var s3 = ppp - pp
    var s0 = 1 - s2
    var s1 = s3 - pp + p

    // Layout of keyframe output values for CUBICSPLINE animations:
    //   [ inTangent_1, splineVertex_1, outTangent_1, inTangent_2, splineVertex_2, ... ]
    for (var i = 0; i !== stride; i++) {
      var p0 = values[offset0 + i + stride] // splineVertex_k
      var m0 = values[offset0 + i + stride2] * td // outTangent_k * (t_k+1 - t_k)
      var p1 = values[offset1 + i + stride] // splineVertex_k+1
      var m1 = values[offset1 + i] * td // inTangent_k+1 * (t_k+1 - t_k)

      result[i] = s0 * p0 + s1 * m0 + s2 * p1 + s3 * m1
    }

    return result
  }

  /*********************************/
  /********** INTERNALS ************/
  /*********************************/

  /* CONSTANTS */

  var WEBGL_CONSTANTS = {
    FLOAT: 5126,
    //FLOAT_MAT2: 35674,
    FLOAT_MAT3: 35675,
    FLOAT_MAT4: 35676,
    FLOAT_VEC2: 35664,
    FLOAT_VEC3: 35665,
    FLOAT_VEC4: 35666,
    LINEAR: 9729,
    REPEAT: 10497,
    SAMPLER_2D: 35678,
    POINTS: 0,
    LINES: 1,
    LINE_LOOP: 2,
    LINE_STRIP: 3,
    TRIANGLES: 4,
    TRIANGLE_STRIP: 5,
    TRIANGLE_FAN: 6,
    UNSIGNED_BYTE: 5121,
    UNSIGNED_SHORT: 5123
  }

  var WEBGL_COMPONENT_TYPES = {
    5120: Int8Array,
    5121: Uint8Array,
    5122: Int16Array,
    5123: Uint16Array,
    5125: Uint32Array,
    5126: Float32Array
  }

  var WEBGL_FILTERS = {
    9728: THREE.NearestFilter,
    9729: THREE.LinearFilter,
    9984: THREE.NearestMipmapNearestFilter,
    9985: THREE.LinearMipmapNearestFilter,
    9986: THREE.NearestMipmapLinearFilter,
    9987: THREE.LinearMipmapLinearFilter
  }

  var WEBGL_WRAPPINGS = {
    33071: THREE.ClampToEdgeWrapping,
    33648: THREE.MirroredRepeatWrapping,
    10497: THREE.RepeatWrapping
  }

  var WEBGL_TYPE_SIZES = {
    SCALAR: 1,
    VEC2: 2,
    VEC3: 3,
    VEC4: 4,
    MAT2: 4,
    MAT3: 9,
    MAT4: 16
  }

  var ATTRIBUTES = {
    POSITION: 'position',
    NORMAL: 'normal',
    TANGENT: 'tangent',
    TEXCOORD_0: 'uv',
    TEXCOORD_1: 'uv2',
    COLOR_0: 'color',
    WEIGHTS_0: 'skinWeight',
    JOINTS_0: 'skinIndex'
  }

  var PATH_PROPERTIES = {
    scale: 'scale',
    translation: 'position',
    rotation: 'quaternion',
    weights: 'morphTargetInfluences'
  }

  var INTERPOLATION = {
    CUBICSPLINE: undefined, // We use a custom interpolant (GLTFCubicSplineInterpolation) for CUBICSPLINE tracks. Each
    // keyframe track will be initialized with a default interpolation type, then modified.
    LINEAR: THREE.InterpolateLinear,
    STEP: THREE.InterpolateDiscrete
  }

  var ALPHA_MODES = {
    OPAQUE: 'OPAQUE',
    MASK: 'MASK',
    BLEND: 'BLEND'
  }

  /* UTILITY FUNCTIONS */

  function resolveURL(url, path) {
    // Invalid URL
    if (typeof url !== 'string' || url === '') return ''

    // Host Relative URL
    if (/^https?:\/\//i.test(path) && /^\//.test(url)) {
      path = path.replace(/(^https?:\/\/[^\/]+).*/i, '$1')
    }

    // Absolute URL http://,https://,//
    if (/^(https?:)?\/\//i.test(url)) return url

    // Data URI
    if (/^data:.*,.*$/i.test(url)) return url

    // Blob URL
    if (/^blob:.*$/i.test(url)) return url

    // Relative URL
    return path + url
  }

  /**
   * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#default-material
   */
  function createDefaultMaterial(cache) {
    if (cache['DefaultMaterial'] === undefined) {
      cache['DefaultMaterial'] = new THREE.MeshStandardMaterial({
        color: 0xffffff,
        emissive: 0x000000,
        metalness: 1,
        roughness: 1,
        transparent: false,
        depthTest: true,
        side: THREE.FrontSide
      })
    }

    return cache['DefaultMaterial']
  }

  function addUnknownExtensionsToUserData(knownExtensions, object, objectDef) {
    // Add unknown glTF extensions to an object's userData.

    for (var name in objectDef.extensions) {
      if (knownExtensions[name] === undefined) {
        object.userData.gltfExtensions = object.userData.gltfExtensions || {}
        object.userData.gltfExtensions[name] = objectDef.extensions[name]
      }
    }
  }

  /**
   * @param {THREE.Object3D|THREE.Material|THREE.BufferGeometry} object
   * @param {GLTF.definition} gltfDef
   */
  function assignExtrasToUserData(object, gltfDef) {
    if (gltfDef.extras !== undefined) {
      if (typeof gltfDef.extras === 'object') {
        Object.assign(object.userData, gltfDef.extras)
      } else {
        console.warn('THREE.GLTFLoader: Ignoring primitive type .extras, ' + gltfDef.extras)
      }
    }
  }

  /**
   * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#morph-targets
   *
   * @param {THREE.BufferGeometry} geometry
   * @param {Array<GLTF.Target>} targets
   * @param {GLTFParser} parser
   * @return {Promise<THREE.BufferGeometry>}
   */
  function addMorphTargets(geometry, targets, parser) {
    var hasMorphPosition = false
    var hasMorphNormal = false

    for (var i = 0, il = targets.length; i < il; i++) {
      var target = targets[i]

      if (target.POSITION !== undefined) hasMorphPosition = true
      if (target.NORMAL !== undefined) hasMorphNormal = true

      if (hasMorphPosition && hasMorphNormal) break
    }

    if (!hasMorphPosition && !hasMorphNormal) return Promise.resolve(geometry)

    var pendingPositionAccessors = []
    var pendingNormalAccessors = []

    for (var i = 0, il = targets.length; i < il; i++) {
      var target = targets[i]

      if (hasMorphPosition) {
        var pendingAccessor = target.POSITION !== undefined ? parser.getDependency('accessor', target.POSITION) : geometry.attributes.position

        pendingPositionAccessors.push(pendingAccessor)
      }

      if (hasMorphNormal) {
        var pendingAccessor = target.NORMAL !== undefined ? parser.getDependency('accessor', target.NORMAL) : geometry.attributes.normal

        pendingNormalAccessors.push(pendingAccessor)
      }
    }

    return Promise.all([Promise.all(pendingPositionAccessors), Promise.all(pendingNormalAccessors)]).then(function(accessors) {
      var morphPositions = accessors[0]
      var morphNormals = accessors[1]

      if (hasMorphPosition) geometry.morphAttributes.position = morphPositions
      if (hasMorphNormal) geometry.morphAttributes.normal = morphNormals
      geometry.morphTargetsRelative = true

      return geometry
    })
  }

  /**
   * @param {THREE.Mesh} mesh
   * @param {GLTF.Mesh} meshDef
   */
  function updateMorphTargets(mesh, meshDef) {
    mesh.updateMorphTargets()

    if (meshDef.weights !== undefined) {
      for (var i = 0, il = meshDef.weights.length; i < il; i++) {
        mesh.morphTargetInfluences[i] = meshDef.weights[i]
      }
    }

    // .extras has user-defined data, so check that .extras.targetNames is an array.
    if (meshDef.extras && Array.isArray(meshDef.extras.targetNames)) {
      var targetNames = meshDef.extras.targetNames

      if (mesh.morphTargetInfluences.length === targetNames.length) {
        mesh.morphTargetDictionary = {}

        for (var i = 0, il = targetNames.length; i < il; i++) {
          mesh.morphTargetDictionary[targetNames[i]] = i
        }
      } else {
        console.warn('THREE.GLTFLoader: Invalid extras.targetNames length. Ignoring names.')
      }
    }
  }

  function createPrimitiveKey(primitiveDef) {
    var dracoExtension = primitiveDef.extensions && primitiveDef.extensions[EXTENSIONS.KHR_DRACO_MESH_COMPRESSION]
    var geometryKey

    if (dracoExtension) {
      geometryKey = 'draco:' + dracoExtension.bufferView + ':' + dracoExtension.indices + ':' + createAttributesKey(dracoExtension.attributes)
    } else {
      geometryKey = primitiveDef.indices + ':' + createAttributesKey(primitiveDef.attributes) + ':' + primitiveDef.mode
    }

    return geometryKey
  }

  function createAttributesKey(attributes) {
    var attributesKey = ''

    var keys = Object.keys(attributes).sort()

    for (var i = 0, il = keys.length; i < il; i++) {
      attributesKey += keys[i] + ':' + attributes[keys[i]] + ';'
    }

    return attributesKey
  }

  /* GLTF PARSER */

  function GLTFParser(json, options) {
    this.json = json || {}
    this.extensions = {}
    this.plugins = {}
    this.options = options || {}

    // loader object cache
    this.cache = new GLTFRegistry()

    // associations between Three.js objects and glTF elements
    this.associations = new Map()

    // BufferGeometry caching
    this.primitiveCache = {}

    // Object3D instance caches
    this.meshCache = { refs: {}, uses: {} }
    this.cameraCache = { refs: {}, uses: {} }
    this.lightCache = { refs: {}, uses: {} }

    // Track node names, to ensure no duplicates
    this.nodeNamesUsed = {}

    // Use an ImageBitmapLoader if imageBitmaps are supported. Moves much of the
    // expensive work of uploading a texture to the GPU off the main thread.
    if (typeof createImageBitmap !== 'undefined' && /Firefox/.test(navigator.userAgent) === false) {
      this.textureLoader = new THREE.ImageBitmapLoader(this.options.manager)
    } else {
      this.textureLoader = new THREE.TextureLoader(this.options.manager)
    }

    this.textureLoader.setCrossOrigin(this.options.crossOrigin)

    this.fileLoader = new THREE.FileLoader(this.options.manager)
    this.fileLoader.setResponseType('arraybuffer')

    if (this.options.crossOrigin === 'use-credentials') {
      this.fileLoader.setWithCredentials(true)
    }
  }

  GLTFParser.prototype.setExtensions = function(extensions) {
    this.extensions = extensions
  }

  GLTFParser.prototype.setPlugins = function(plugins) {
    this.plugins = plugins
  }

  GLTFParser.prototype.parse = function(onLoad, onError) {
    var parser = this
    var json = this.json
    var extensions = this.extensions

    // Clear the loader cache
    this.cache.removeAll()

    // Mark the special nodes/meshes in json for efficient parse
    this._invokeAll(function(ext) {
      return ext._markDefs && ext._markDefs()
    })

    Promise.all([this.getDependencies('scene'), this.getDependencies('animation'), this.getDependencies('camera')])
      .then(function(dependencies) {
        var result = {
          scene: dependencies[0][json.scene || 0],
          scenes: dependencies[0],
          animations: dependencies[1],
          cameras: dependencies[2],
          asset: json.asset,
          parser: parser,
          userData: {}
        }

        addUnknownExtensionsToUserData(extensions, result, json)

        assignExtrasToUserData(result, json)

        onLoad(result)
      })
      .catch(onError)
  }

  /**
   * Marks the special nodes/meshes in json for efficient parse.
   */
  GLTFParser.prototype._markDefs = function() {
    var nodeDefs = this.json.nodes || []
    var skinDefs = this.json.skins || []
    var meshDefs = this.json.meshes || []

    // Nothing in the node definition indicates whether it is a Bone or an
    // Object3D. Use the skins' joint references to mark bones.
    for (var skinIndex = 0, skinLength = skinDefs.length; skinIndex < skinLength; skinIndex++) {
      var joints = skinDefs[skinIndex].joints

      for (var i = 0, il = joints.length; i < il; i++) {
        nodeDefs[joints[i]].isBone = true
      }
    }

    // Iterate over all nodes, marking references to shared resources,
    // as well as skeleton joints.
    for (var nodeIndex = 0, nodeLength = nodeDefs.length; nodeIndex < nodeLength; nodeIndex++) {
      var nodeDef = nodeDefs[nodeIndex]

      if (nodeDef.mesh !== undefined) {
        this._addNodeRef(this.meshCache, nodeDef.mesh)

        // Nothing in the mesh definition indicates whether it is
        // a SkinnedMesh or Mesh. Use the node's mesh reference
        // to mark SkinnedMesh if node has skin.
        if (nodeDef.skin !== undefined) {
          meshDefs[nodeDef.mesh].isSkinnedMesh = true
        }
      }

      if (nodeDef.camera !== undefined) {
        this._addNodeRef(this.cameraCache, nodeDef.camera)
      }
    }
  }

  /**
   * Counts references to shared node / Object3D resources. These resources
   * can be reused, or "instantiated", at multiple nodes in the scene
   * hierarchy. Mesh, Camera, and Light instances are instantiated and must
   * be marked. Non-scenegraph resources (like Materials, Geometries, and
   * Textures) can be reused directly and are not marked here.
   *
   * Example: CesiumMilkTruck sample model reuses "Wheel" meshes.
   */
  GLTFParser.prototype._addNodeRef = function(cache, index) {
    if (index === undefined) return

    if (cache.refs[index] === undefined) {
      cache.refs[index] = cache.uses[index] = 0
    }

    cache.refs[index]++
  }

  /** Returns a reference to a shared resource, cloning it if necessary. */
  GLTFParser.prototype._getNodeRef = function(cache, index, object) {
    if (cache.refs[index] <= 1) return object

    var ref = object.clone()

    ref.name += '_instance_' + cache.uses[index]++

    return ref
  }

  GLTFParser.prototype._invokeOne = function(func) {
    var extensions = Object.values(this.plugins)
    extensions.push(this)

    for (var i = 0; i < extensions.length; i++) {
      var result = func(extensions[i])

      if (result) return result
    }
  }

  GLTFParser.prototype._invokeAll = function(func) {
    var extensions = Object.values(this.plugins)
    extensions.unshift(this)

    var pending = []

    for (var i = 0; i < extensions.length; i++) {
      var result = func(extensions[i])

      if (result) pending.push(result)
    }

    return pending
  }

  /**
   * Requests the specified dependency asynchronously, with caching.
   * @param {string} type
   * @param {number} index
   * @return {Promise<THREE.Object3D|THREE.Material|THREE.Texture|THREE.AnimationClip|ArrayBuffer|Object>}
   */
  GLTFParser.prototype.getDependency = function(type, index) {
    var cacheKey = type + ':' + index
    var dependency = this.cache.get(cacheKey)

    if (!dependency) {
      switch (type) {
        case 'scene':
          dependency = this.loadScene(index)
          break

        case 'node':
          dependency = this.loadNode(index)
          break

        case 'mesh':
          dependency = this._invokeOne(function(ext) {
            return ext.loadMesh && ext.loadMesh(index)
          })
          break

        case 'accessor':
          dependency = this.loadAccessor(index)
          break

        case 'bufferView':
          dependency = this._invokeOne(function(ext) {
            return ext.loadBufferView && ext.loadBufferView(index)
          })
          break

        case 'buffer':
          dependency = this.loadBuffer(index)
          break

        case 'material':
          dependency = this._invokeOne(function(ext) {
            return ext.loadMaterial && ext.loadMaterial(index)
          })
          break

        case 'texture':
          dependency = this._invokeOne(function(ext) {
            return ext.loadTexture && ext.loadTexture(index)
          })
          break

        case 'skin':
          dependency = this.loadSkin(index)
          break

        case 'animation':
          dependency = this.loadAnimation(index)
          break

        case 'camera':
          dependency = this.loadCamera(index)
          break

        default:
          throw new Error('Unknown type: ' + type)
      }

      this.cache.add(cacheKey, dependency)
    }

    return dependency
  }

  /**
   * Requests all dependencies of the specified type asynchronously, with caching.
   * @param {string} type
   * @return {Promise<Array<Object>>}
   */
  GLTFParser.prototype.getDependencies = function(type) {
    var dependencies = this.cache.get(type)

    if (!dependencies) {
      var parser = this
      var defs = this.json[type + (type === 'mesh' ? 'es' : 's')] || []

      dependencies = Promise.all(
        defs.map(function(def, index) {
          return parser.getDependency(type, index)
        })
      )

      this.cache.add(type, dependencies)
    }

    return dependencies
  }

  /**
   * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#buffers-and-buffer-views
   * @param {number} bufferIndex
   * @return {Promise<ArrayBuffer>}
   */
  GLTFParser.prototype.loadBuffer = function(bufferIndex) {
    var bufferDef = this.json.buffers[bufferIndex]
    var loader = this.fileLoader

    if (bufferDef.type && bufferDef.type !== 'arraybuffer') {
      throw new Error('THREE.GLTFLoader: ' + bufferDef.type + ' buffer type is not supported.')
    }

    // If present, GLB container is required to be the first buffer.
    if (bufferDef.uri === undefined && bufferIndex === 0) {
      return Promise.resolve(this.extensions[EXTENSIONS.KHR_BINARY_GLTF].body)
    }

    var options = this.options

    return new Promise(function(resolve, reject) {
      loader.load(resolveURL(bufferDef.uri, options.path), resolve, undefined, function() {
        reject(new Error('THREE.GLTFLoader: Failed to load buffer "' + bufferDef.uri + '".'))
      })
    })
  }

  /**
   * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#buffers-and-buffer-views
   * @param {number} bufferViewIndex
   * @return {Promise<ArrayBuffer>}
   */
  GLTFParser.prototype.loadBufferView = function(bufferViewIndex) {
    var bufferViewDef = this.json.bufferViews[bufferViewIndex]

    return this.getDependency('buffer', bufferViewDef.buffer).then(function(buffer) {
      var byteLength = bufferViewDef.byteLength || 0
      var byteOffset = bufferViewDef.byteOffset || 0
      return buffer.slice(byteOffset, byteOffset + byteLength)
    })
  }

  /**
   * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#accessors
   * @param {number} accessorIndex
   * @return {Promise<THREE.BufferAttribute|THREE.InterleavedBufferAttribute>}
   */
  GLTFParser.prototype.loadAccessor = function(accessorIndex) {
    var parser = this
    var json = this.json

    var accessorDef = this.json.accessors[accessorIndex]

    if (accessorDef.bufferView === undefined && accessorDef.sparse === undefined) {
      // Ignore empty accessors, which may be used to declare runtime
      // information about attributes coming from another source (e.g. Draco
      // compression extension).
      return Promise.resolve(null)
    }

    var pendingBufferViews = []

    if (accessorDef.bufferView !== undefined) {
      pendingBufferViews.push(this.getDependency('bufferView', accessorDef.bufferView))
    } else {
      pendingBufferViews.push(null)
    }

    if (accessorDef.sparse !== undefined) {
      pendingBufferViews.push(this.getDependency('bufferView', accessorDef.sparse.indices.bufferView))
      pendingBufferViews.push(this.getDependency('bufferView', accessorDef.sparse.values.bufferView))
    }

    return Promise.all(pendingBufferViews).then(function(bufferViews) {
      var bufferView = bufferViews[0]

      var itemSize = WEBGL_TYPE_SIZES[accessorDef.type]
      var TypedArray = WEBGL_COMPONENT_TYPES[accessorDef.componentType]

      // For VEC3: itemSize is 3, elementBytes is 4, itemBytes is 12.
      var elementBytes = TypedArray.BYTES_PER_ELEMENT
      var itemBytes = elementBytes * itemSize
      var byteOffset = accessorDef.byteOffset || 0
      var byteStride = accessorDef.bufferView !== undefined ? json.bufferViews[accessorDef.bufferView].byteStride : undefined
      var normalized = accessorDef.normalized === true
      var array, bufferAttribute

      // The buffer is not interleaved if the stride is the item size in bytes.
      if (byteStride && byteStride !== itemBytes) {
        // Each "slice" of the buffer, as defined by 'count' elements of 'byteStride' bytes, gets its own InterleavedBuffer
        // This makes sure that IBA.count reflects accessor.count properly
        var ibSlice = Math.floor(byteOffset / byteStride)
        var ibCacheKey = 'InterleavedBuffer:' + accessorDef.bufferView + ':' + accessorDef.componentType + ':' + ibSlice + ':' + accessorDef.count
        var ib = parser.cache.get(ibCacheKey)

        if (!ib) {
          array = new TypedArray(bufferView, ibSlice * byteStride, (accessorDef.count * byteStride) / elementBytes)

          // Integer parameters to IB/IBA are in array elements, not bytes.
          ib = new THREE.InterleavedBuffer(array, byteStride / elementBytes)

          parser.cache.add(ibCacheKey, ib)
        }

        bufferAttribute = new THREE.InterleavedBufferAttribute(ib, itemSize, (byteOffset % byteStride) / elementBytes, normalized)
      } else {
        if (bufferView === null) {
          array = new TypedArray(accessorDef.count * itemSize)
        } else {
          array = new TypedArray(bufferView, byteOffset, accessorDef.count * itemSize)
        }

        bufferAttribute = new THREE.BufferAttribute(array, itemSize, normalized)
      }

      // https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#sparse-accessors
      if (accessorDef.sparse !== undefined) {
        var itemSizeIndices = WEBGL_TYPE_SIZES.SCALAR
        var TypedArrayIndices = WEBGL_COMPONENT_TYPES[accessorDef.sparse.indices.componentType]

        var byteOffsetIndices = accessorDef.sparse.indices.byteOffset || 0
        var byteOffsetValues = accessorDef.sparse.values.byteOffset || 0

        var sparseIndices = new TypedArrayIndices(bufferViews[1], byteOffsetIndices, accessorDef.sparse.count * itemSizeIndices)
        var sparseValues = new TypedArray(bufferViews[2], byteOffsetValues, accessorDef.sparse.count * itemSize)

        if (bufferView !== null) {
          // Avoid modifying the original ArrayBuffer, if the bufferView wasn't initialized with zeroes.
          bufferAttribute = new THREE.BufferAttribute(bufferAttribute.array.slice(), bufferAttribute.itemSize, bufferAttribute.normalized)
        }

        for (var i = 0, il = sparseIndices.length; i < il; i++) {
          var index = sparseIndices[i]

          bufferAttribute.setX(index, sparseValues[i * itemSize])
          if (itemSize >= 2) bufferAttribute.setY(index, sparseValues[i * itemSize + 1])
          if (itemSize >= 3) bufferAttribute.setZ(index, sparseValues[i * itemSize + 2])
          if (itemSize >= 4) bufferAttribute.setW(index, sparseValues[i * itemSize + 3])
          if (itemSize >= 5) throw new Error('THREE.GLTFLoader: Unsupported itemSize in sparse BufferAttribute.')
        }
      }

      return bufferAttribute
    })
  }

  /**
   * Specification: https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#textures
   * @param {number} textureIndex
   * @return {Promise<THREE.Texture>}
   */
  GLTFParser.prototype.loadTexture = function(textureIndex) {
    var parser = this
    var json = this.json
    var options = this.options

    var textureDef = json.textures[textureIndex]

    var textureExtensions = textureDef.extensions || {}

    var source

    if (textureExtensions[EXTENSIONS.MSFT_TEXTURE_DDS]) {
      source = json.images[textureExtensions[EXTENSIONS.MSFT_TEXTURE_DDS].source]
    } else {
      source = json.images[textureDef.source]
    }

    var loader

    if (source.uri) {
      loader = options.manager.getHandler(source.uri)
    }

    if (!loader) {
      loader = textureExtensions[EXTENSIONS.MSFT_TEXTURE_DDS] ? parser.extensions[EXTENSIONS.MSFT_TEXTURE_DDS].ddsLoader : this.textureLoader
    }

    return this.loadTextureImage(textureIndex, source, loader)
  }

  GLTFParser.prototype.loadTextureImage = function(textureIndex, source, loader) {
    var parser = this
    var json = this.json
    var options = this.options

    var textureDef = json.textures[textureIndex]

    var URL = self.URL || self.webkitURL

    var sourceURI = source.uri
    var isObjectURL = false
    var hasAlpha = true

    if (source.mimeType === 'image/jpeg') hasAlpha = false

    if (source.bufferView !== undefined) {
      // Load binary image data from bufferView, if provided.

      sourceURI = parser.getDependency('bufferView', source.bufferView).then(function(bufferView) {
        if (source.mimeType === 'image/png') {
          // Inspect the PNG 'IHDR' chunk to determine whether the image could have an
          // alpha channel. This check is conservative — the image could have an alpha
          // channel with all values == 1, and the indexed type (colorType == 3) only
          // sometimes contains alpha.
          //
          // https://en.wikipedia.org/wiki/Portable_Network_Graphics#File_header
          var colorType = new DataView(bufferView, 25, 1).getUint8(0, false)
          hasAlpha = colorType === 6 || colorType === 4 || colorType === 3
        }

        isObjectURL = true
        var blob = new Blob([bufferView], { type: source.mimeType })
        sourceURI = URL.createObjectURL(blob)
        return sourceURI
      })
    }

    return Promise.resolve(sourceURI)
      .then(function(sourceURI) {
        return new Promise(function(resolve, reject) {
          var onLoad = resolve

          if (loader.isImageBitmapLoader === true) {
            onLoad = function(imageBitmap) {
              resolve(new THREE.CanvasTexture(imageBitmap))
            }
          }

          loader.load(resolveURL(sourceURI, options.path), onLoad, undefined, reject)
        })
      })
      .then(function(texture) {
        // Clean up resources and configure Texture.

        if (isObjectURL === true) {
          URL.revokeObjectURL(sourceURI)
        }

        texture.flipY = false

        if (textureDef.name) texture.name = textureDef.name

        // When there is definitely no alpha channel in the texture, set RGBFormat to save space.
        if (!hasAlpha) texture.format = THREE.RGBFormat

        var samplers = json.samplers || {}
        var sampler = samplers[textureDef.sampler] || {}

        texture.magFilter = WEBGL_FILTERS[sampler.magFilter] || THREE.LinearFilter
        texture.minFilter = WEBGL_FILTERS[sampler.minFilter] || THREE.LinearMipmapLinearFilter
        texture.wrapS = WEBGL_WRAPPINGS[sampler.wrapS] || THREE.RepeatWrapping
        texture.wrapT = WEBGL_WRAPPINGS[sampler.wrapT] || THREE.RepeatWrapping

        parser.associations.set(texture, {
          type: 'textures',
          index: textureIndex
        })

        return texture
      })
  }

  /**
   * Asynchronously assigns a texture to the given material parameters.
   * @param {Object} materialParams
   * @param {string} mapName
   * @param {Object} mapDef
   * @return {Promise}
   */
  GLTFParser.prototype.assignTexture = function(materialParams, mapName, mapDef) {
    var parser = this

    return this.getDependency('texture', mapDef.index).then(function(texture) {
      // Materials sample aoMap from UV set 1 and other maps from UV set 0 - this can't be configured
      // However, we will copy UV set 0 to UV set 1 on demand for aoMap
      if (mapDef.texCoord !== undefined && mapDef.texCoord != 0 && !(mapName === 'aoMap' && mapDef.texCoord == 1)) {
        console.warn('THREE.GLTFLoader: Custom UV set ' + mapDef.texCoord + ' for texture ' + mapName + ' not yet supported.')
      }

      if (parser.extensions[EXTENSIONS.KHR_TEXTURE_TRANSFORM]) {
        var transform = mapDef.extensions !== undefined ? mapDef.extensions[EXTENSIONS.KHR_TEXTURE_TRANSFORM] : undefined

        if (transform) {
          var gltfReference = parser.associations.get(texture)
          texture = parser.extensions[EXTENSIONS.KHR_TEXTURE_TRANSFORM].extendTexture(texture, transform)
          parser.associations.set(texture, gltfReference)
        }
      }

      materialParams[mapName] = texture
    })
  }

  /**
   * Assigns final material to a Mesh, Line, or Points instance. The instance
   * already has a material (generated from the glTF material options alone)
   * but reuse of the same glTF material may require multiple threejs materials
   * to accomodate different primitive types, defines, etc. New materials will
   * be created if necessary, and reused from a cache.
   * @param  {THREE.Object3D} mesh Mesh, Line, or Points instance.
   */
  GLTFParser.prototype.assignFinalMaterial = function(mesh) {
    var geometry = mesh.geometry
    var material = mesh.material

    var useVertexTangents = geometry.attributes.tangent !== undefined
    var useVertexColors = geometry.attributes.color !== undefined
    var useFlatShading = geometry.attributes.normal === undefined
    var useSkinning = mesh.isSkinnedMesh === true
    var useMorphTargets = Object.keys(geometry.morphAttributes).length > 0
    var useMorphNormals = useMorphTargets && geometry.morphAttributes.normal !== undefined

    if (mesh.isPoints) {
      var cacheKey = 'PointsMaterial:' + material.uuid

      var pointsMaterial = this.cache.get(cacheKey)

      if (!pointsMaterial) {
        pointsMaterial = new THREE.PointsMaterial()
        THREE.Material.prototype.copy.call(pointsMaterial, material)
        pointsMaterial.color.copy(material.color)
        pointsMaterial.map = material.map
        pointsMaterial.sizeAttenuation = false // glTF spec says points should be 1px

        this.cache.add(cacheKey, pointsMaterial)
      }

      material = pointsMaterial
    } else if (mesh.isLine) {
      var cacheKey = 'LineBasicMaterial:' + material.uuid

      var lineMaterial = this.cache.get(cacheKey)

      if (!lineMaterial) {
        lineMaterial = new THREE.LineBasicMaterial()
        THREE.Material.prototype.copy.call(lineMaterial, material)
        lineMaterial.color.copy(material.color)

        this.cache.add(cacheKey, lineMaterial)
      }

      material = lineMaterial
    }

    // Clone the material if it will be modified
    if (useVertexTangents || useVertexColors || useFlatShading || useSkinning || useMorphTargets) {
      var cacheKey = 'ClonedMaterial:' + material.uuid + ':'

      if (material.isGLTFSpecularGlossinessMaterial) cacheKey += 'specular-glossiness:'
      if (useSkinning) cacheKey += 'skinning:'
      if (useVertexTangents) cacheKey += 'vertex-tangents:'
      if (useVertexColors) cacheKey += 'vertex-colors:'
      if (useFlatShading) cacheKey += 'flat-shading:'
      if (useMorphTargets) cacheKey += 'morph-targets:'
      if (useMorphNormals) cacheKey += 'morph-normals:'

      var cachedMaterial = this.cache.get(cacheKey)

      if (!cachedMaterial) {
        cachedMaterial = material.clone()

        if (useSkinning) cachedMaterial.skinning = true
        if (useVertexTangents) cachedMaterial.vertexTangents = true
        if (useVertexColors) cachedMaterial.vertexColors = true
        if (useFlatShading) cachedMaterial.flatShading = true
        if (useMorphTargets) cachedMaterial.morphTargets = true
        if (useMorphNormals) cachedMaterial.morphNormals = true

        this.cache.add(cacheKey, cachedMaterial)

        this.associations.set(cachedMaterial, this.associations.get(material))
      }

      material = cachedMaterial
    }

    // workarounds for mesh and geometry

    if (material.aoMap && geometry.attributes.uv2 === undefined && geometry.attributes.uv !== undefined) {
      geometry.setAttribute('uv2', geometry.attributes.uv)
    }

    // https://github.com/mrdoob/three.js/issues/11438#issuecomment-507003995
    if (material.normalScale && !useVertexTangents) {
      material.normalScale.y = -material.normalScale.y
    }

    if (material.clearcoatNormalScale && !useVertexTangents) {
      material.clearcoatNormalScale.y = -material.clearcoatNormalScale.y
    }

    mesh.material = material
  }

  GLTFParser.prototype.getMaterialType = function(/* materialIndex */) {
    return THREE.MeshStandardMaterial
  }

  /**
   * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#materials
   * @param {number} materialIndex
   * @return {Promise<THREE.Material>}
   */
  GLTFParser.prototype.loadMaterial = function(materialIndex) {
    var parser = this
    var json = this.json
    var extensions = this.extensions
    var materialDef = json.materials[materialIndex]

    var materialType
    var materialParams = {}
    var materialExtensions = materialDef.extensions || {}

    var pending = []

    if (materialExtensions[EXTENSIONS.KHR_MATERIALS_PBR_SPECULAR_GLOSSINESS]) {
      var sgExtension = extensions[EXTENSIONS.KHR_MATERIALS_PBR_SPECULAR_GLOSSINESS]
      materialType = sgExtension.getMaterialType()
      pending.push(sgExtension.extendParams(materialParams, materialDef, parser))
    } else if (materialExtensions[EXTENSIONS.KHR_MATERIALS_UNLIT]) {
      var kmuExtension = extensions[EXTENSIONS.KHR_MATERIALS_UNLIT]
      materialType = kmuExtension.getMaterialType()
      pending.push(kmuExtension.extendParams(materialParams, materialDef, parser))
    } else {
      // Specification:
      // https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#metallic-roughness-material

      var metallicRoughness = materialDef.pbrMetallicRoughness || {}

      materialParams.color = new THREE.Color(1.0, 1.0, 1.0)
      materialParams.opacity = 1.0

      if (Array.isArray(metallicRoughness.baseColorFactor)) {
        var array = metallicRoughness.baseColorFactor

        materialParams.color.fromArray(array)
        materialParams.opacity = array[3]
      }

      if (metallicRoughness.baseColorTexture !== undefined) {
        pending.push(parser.assignTexture(materialParams, 'map', metallicRoughness.baseColorTexture))
      }

      materialParams.metalness = metallicRoughness.metallicFactor !== undefined ? metallicRoughness.metallicFactor : 1.0
      materialParams.roughness = metallicRoughness.roughnessFactor !== undefined ? metallicRoughness.roughnessFactor : 1.0

      if (metallicRoughness.metallicRoughnessTexture !== undefined) {
        pending.push(parser.assignTexture(materialParams, 'metalnessMap', metallicRoughness.metallicRoughnessTexture))
        pending.push(parser.assignTexture(materialParams, 'roughnessMap', metallicRoughness.metallicRoughnessTexture))
      }

      materialType = this._invokeOne(function(ext) {
        return ext.getMaterialType && ext.getMaterialType(materialIndex)
      })

      pending.push(
        Promise.all(
          this._invokeAll(function(ext) {
            return ext.extendMaterialParams && ext.extendMaterialParams(materialIndex, materialParams)
          })
        )
      )
    }

    if (materialDef.doubleSided === true) {
      materialParams.side = THREE.DoubleSide
    }

    var alphaMode = materialDef.alphaMode || ALPHA_MODES.OPAQUE

    if (alphaMode === ALPHA_MODES.BLEND) {
      materialParams.transparent = true

      // See: https://github.com/mrdoob/three.js/issues/17706
      materialParams.depthWrite = false
    } else {
      materialParams.transparent = false

      if (alphaMode === ALPHA_MODES.MASK) {
        materialParams.alphaTest = materialDef.alphaCutoff !== undefined ? materialDef.alphaCutoff : 0.5
      }
    }

    if (materialDef.normalTexture !== undefined && materialType !== THREE.MeshBasicMaterial) {
      pending.push(parser.assignTexture(materialParams, 'normalMap', materialDef.normalTexture))

      materialParams.normalScale = new THREE.Vector2(1, 1)

      if (materialDef.normalTexture.scale !== undefined) {
        materialParams.normalScale.set(materialDef.normalTexture.scale, materialDef.normalTexture.scale)
      }
    }

    if (materialDef.occlusionTexture !== undefined && materialType !== THREE.MeshBasicMaterial) {
      pending.push(parser.assignTexture(materialParams, 'aoMap', materialDef.occlusionTexture))

      if (materialDef.occlusionTexture.strength !== undefined) {
        materialParams.aoMapIntensity = materialDef.occlusionTexture.strength
      }
    }

    if (materialDef.emissiveFactor !== undefined && materialType !== THREE.MeshBasicMaterial) {
      materialParams.emissive = new THREE.Color().fromArray(materialDef.emissiveFactor)
    }

    if (materialDef.emissiveTexture !== undefined && materialType !== THREE.MeshBasicMaterial) {
      pending.push(parser.assignTexture(materialParams, 'emissiveMap', materialDef.emissiveTexture))
    }

    return Promise.all(pending).then(function() {
      var material

      if (materialType === GLTFMeshStandardSGMaterial) {
        material = extensions[EXTENSIONS.KHR_MATERIALS_PBR_SPECULAR_GLOSSINESS].createMaterial(materialParams)
      } else {
        material = new materialType(materialParams)
      }

      if (materialDef.name) material.name = materialDef.name

      // baseColorTexture, emissiveTexture, and specularGlossinessTexture use sRGB encoding.
      if (material.map) material.map.encoding = THREE.sRGBEncoding
      if (material.emissiveMap) material.emissiveMap.encoding = THREE.sRGBEncoding

      assignExtrasToUserData(material, materialDef)

      parser.associations.set(material, { type: 'materials', index: materialIndex })

      if (materialDef.extensions) addUnknownExtensionsToUserData(extensions, material, materialDef)

      return material
    })
  }

  /** When Object3D instances are targeted by animation, they need unique names. */
  GLTFParser.prototype.createUniqueName = function(originalName) {
    var name = THREE.PropertyBinding.sanitizeNodeName(originalName || '')

    for (var i = 1; this.nodeNamesUsed[name]; ++i) {
      name = originalName + '_' + i
    }

    this.nodeNamesUsed[name] = true

    return name
  }

  /**
   * @param {THREE.BufferGeometry} geometry
   * @param {GLTF.Primitive} primitiveDef
   * @param {GLTFParser} parser
   */
  function computeBounds(geometry, primitiveDef, parser) {
    var attributes = primitiveDef.attributes

    var box = new THREE.Box3()

    if (attributes.POSITION !== undefined) {
      var accessor = parser.json.accessors[attributes.POSITION]

      var min = accessor.min
      var max = accessor.max

      // glTF requires 'min' and 'max', but VRM (which extends glTF) currently ignores that requirement.

      if (min !== undefined && max !== undefined) {
        box.set(new THREE.Vector3(min[0], min[1], min[2]), new THREE.Vector3(max[0], max[1], max[2]))
      } else {
        console.warn('THREE.GLTFLoader: Missing min/max properties for accessor POSITION.')

        return
      }
    } else {
      return
    }

    var targets = primitiveDef.targets

    if (targets !== undefined) {
      var maxDisplacement = new THREE.Vector3()
      var vector = new THREE.Vector3()

      for (var i = 0, il = targets.length; i < il; i++) {
        var target = targets[i]

        if (target.POSITION !== undefined) {
          var accessor = parser.json.accessors[target.POSITION]
          var min = accessor.min
          var max = accessor.max

          // glTF requires 'min' and 'max', but VRM (which extends glTF) currently ignores that requirement.

          if (min !== undefined && max !== undefined) {
            // we need to get max of absolute components because target weight is [-1,1]
            vector.setX(Math.max(Math.abs(min[0]), Math.abs(max[0])))
            vector.setY(Math.max(Math.abs(min[1]), Math.abs(max[1])))
            vector.setZ(Math.max(Math.abs(min[2]), Math.abs(max[2])))

            // Note: this assumes that the sum of all weights is at most 1. This isn't quite correct - it's more conservative
            // to assume that each target can have a max weight of 1. However, for some use cases - notably, when morph targets
            // are used to implement key-frame animations and as such only two are active at a time - this results in very large
            // boxes. So for now we make a box that's sometimes a touch too small but is hopefully mostly of reasonable size.
            maxDisplacement.max(vector)
          } else {
            console.warn('THREE.GLTFLoader: Missing min/max properties for accessor POSITION.')
          }
        }
      }

      // As per comment above this box isn't conservative, but has a reasonable size for a very large number of morph targets.
      box.expandByVector(maxDisplacement)
    }

    geometry.boundingBox = box

    var sphere = new THREE.Sphere()

    box.getCenter(sphere.center)
    sphere.radius = box.min.distanceTo(box.max) / 2

    geometry.boundingSphere = sphere
  }

  /**
   * @param {THREE.BufferGeometry} geometry
   * @param {GLTF.Primitive} primitiveDef
   * @param {GLTFParser} parser
   * @return {Promise<THREE.BufferGeometry>}
   */
  function addPrimitiveAttributes(geometry, primitiveDef, parser) {
    var attributes = primitiveDef.attributes

    var pending = []

    function assignAttributeAccessor(accessorIndex, attributeName) {
      return parser.getDependency('accessor', accessorIndex).then(function(accessor) {
        geometry.setAttribute(attributeName, accessor)
      })
    }

    for (var gltfAttributeName in attributes) {
      var threeAttributeName = ATTRIBUTES[gltfAttributeName] || gltfAttributeName.toLowerCase()

      // Skip attributes already provided by e.g. Draco extension.
      if (threeAttributeName in geometry.attributes) continue

      pending.push(assignAttributeAccessor(attributes[gltfAttributeName], threeAttributeName))
    }

    if (primitiveDef.indices !== undefined && !geometry.index) {
      var accessor = parser.getDependency('accessor', primitiveDef.indices).then(function(accessor) {
        geometry.setIndex(accessor)
      })

      pending.push(accessor)
    }

    assignExtrasToUserData(geometry, primitiveDef)

    computeBounds(geometry, primitiveDef, parser)

    return Promise.all(pending).then(function() {
      return primitiveDef.targets !== undefined ? addMorphTargets(geometry, primitiveDef.targets, parser) : geometry
    })
  }

  /**
   * @param {THREE.BufferGeometry} geometry
   * @param {Number} drawMode
   * @return {THREE.BufferGeometry}
   */
  function toTrianglesDrawMode(geometry, drawMode) {
    var index = geometry.getIndex()

    // generate index if not present

    if (index === null) {
      var indices = []

      var position = geometry.getAttribute('position')

      if (position !== undefined) {
        for (var i = 0; i < position.count; i++) {
          indices.push(i)
        }

        geometry.setIndex(indices)
        index = geometry.getIndex()
      } else {
        console.error('THREE.GLTFLoader.toTrianglesDrawMode(): Undefined position attribute. Processing not possible.')
        return geometry
      }
    }

    //

    var numberOfTriangles = index.count - 2
    var newIndices = []

    if (drawMode === THREE.TriangleFanDrawMode) {
      // gl.TRIANGLE_FAN

      for (var i = 1; i <= numberOfTriangles; i++) {
        newIndices.push(index.getX(0))
        newIndices.push(index.getX(i))
        newIndices.push(index.getX(i + 1))
      }
    } else {
      // gl.TRIANGLE_STRIP

      for (var i = 0; i < numberOfTriangles; i++) {
        if (i % 2 === 0) {
          newIndices.push(index.getX(i))
          newIndices.push(index.getX(i + 1))
          newIndices.push(index.getX(i + 2))
        } else {
          newIndices.push(index.getX(i + 2))
          newIndices.push(index.getX(i + 1))
          newIndices.push(index.getX(i))
        }
      }
    }

    if (newIndices.length / 3 !== numberOfTriangles) {
      console.error('THREE.GLTFLoader.toTrianglesDrawMode(): Unable to generate correct amount of triangles.')
    }

    // build final geometry

    var newGeometry = geometry.clone()
    newGeometry.setIndex(newIndices)

    return newGeometry
  }

  /**
   * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#geometry
   *
   * Creates BufferGeometries from primitives.
   *
   * @param {Array<GLTF.Primitive>} primitives
   * @return {Promise<Array<THREE.BufferGeometry>>}
   */
  GLTFParser.prototype.loadGeometries = function(primitives) {
    var parser = this
    var extensions = this.extensions
    var cache = this.primitiveCache

    function createDracoPrimitive(primitive) {
      return extensions[EXTENSIONS.KHR_DRACO_MESH_COMPRESSION].decodePrimitive(primitive, parser).then(function(geometry) {
        return addPrimitiveAttributes(geometry, primitive, parser)
      })
    }

    var pending = []

    for (var i = 0, il = primitives.length; i < il; i++) {
      var primitive = primitives[i]
      var cacheKey = createPrimitiveKey(primitive)

      // See if we've already created this geometry
      var cached = cache[cacheKey]

      if (cached) {
        // Use the cached geometry if it exists
        pending.push(cached.promise)
      } else {
        var geometryPromise

        if (primitive.extensions && primitive.extensions[EXTENSIONS.KHR_DRACO_MESH_COMPRESSION]) {
          // Use DRACO geometry if available
          geometryPromise = createDracoPrimitive(primitive)
        } else {
          // Otherwise create a new geometry
          geometryPromise = addPrimitiveAttributes(new THREE.BufferGeometry(), primitive, parser)
        }

        // Cache this geometry
        cache[cacheKey] = { primitive: primitive, promise: geometryPromise }

        pending.push(geometryPromise)
      }
    }

    return Promise.all(pending)
  }

  /**
   * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#meshes
   * @param {number} meshIndex
   * @return {Promise<THREE.Group|THREE.Mesh|THREE.SkinnedMesh>}
   */
  GLTFParser.prototype.loadMesh = function(meshIndex) {
    var parser = this
    var json = this.json
    var extensions = this.extensions

    var meshDef = json.meshes[meshIndex]
    var primitives = meshDef.primitives

    var pending = []

    for (var i = 0, il = primitives.length; i < il; i++) {
      var material = primitives[i].material === undefined ? createDefaultMaterial(this.cache) : this.getDependency('material', primitives[i].material)

      pending.push(material)
    }

    pending.push(parser.loadGeometries(primitives))

    return Promise.all(pending).then(function(results) {
      var materials = results.slice(0, results.length - 1)
      var geometries = results[results.length - 1]

      var meshes = []

      for (var i = 0, il = geometries.length; i < il; i++) {
        var geometry = geometries[i]
        var primitive = primitives[i]

        // 1. create Mesh

        var mesh

        var material = materials[i]

        if (
          primitive.mode === WEBGL_CONSTANTS.TRIANGLES ||
          primitive.mode === WEBGL_CONSTANTS.TRIANGLE_STRIP ||
          primitive.mode === WEBGL_CONSTANTS.TRIANGLE_FAN ||
          primitive.mode === undefined
        ) {
          // .isSkinnedMesh isn't in glTF spec. See ._markDefs()
          mesh = meshDef.isSkinnedMesh === true ? new THREE.SkinnedMesh(geometry, material) : new THREE.Mesh(geometry, material)

          if (mesh.isSkinnedMesh === true && !mesh.geometry.attributes.skinWeight.normalized) {
            // we normalize floating point skin weight array to fix malformed assets (see #15319)
            // it's important to skip this for non-float32 data since normalizeSkinWeights assumes non-normalized inputs
            mesh.normalizeSkinWeights()
          }

          if (primitive.mode === WEBGL_CONSTANTS.TRIANGLE_STRIP) {
            mesh.geometry = toTrianglesDrawMode(mesh.geometry, THREE.TriangleStripDrawMode)
          } else if (primitive.mode === WEBGL_CONSTANTS.TRIANGLE_FAN) {
            mesh.geometry = toTrianglesDrawMode(mesh.geometry, THREE.TriangleFanDrawMode)
          }
        } else if (primitive.mode === WEBGL_CONSTANTS.LINES) {
          mesh = new THREE.LineSegments(geometry, material)
        } else if (primitive.mode === WEBGL_CONSTANTS.LINE_STRIP) {
          mesh = new THREE.Line(geometry, material)
        } else if (primitive.mode === WEBGL_CONSTANTS.LINE_LOOP) {
          mesh = new THREE.LineLoop(geometry, material)
        } else if (primitive.mode === WEBGL_CONSTANTS.POINTS) {
          mesh = new THREE.Points(geometry, material)
        } else {
          throw new Error('THREE.GLTFLoader: Primitive mode unsupported: ' + primitive.mode)
        }

        if (Object.keys(mesh.geometry.morphAttributes).length > 0) {
          updateMorphTargets(mesh, meshDef)
        }

        mesh.name = parser.createUniqueName(meshDef.name || 'mesh_' + meshIndex)

        assignExtrasToUserData(mesh, meshDef)

        if (primitive.extensions) addUnknownExtensionsToUserData(extensions, mesh, primitive)

        parser.assignFinalMaterial(mesh)

        meshes.push(mesh)
      }

      if (meshes.length === 1) {
        return meshes[0]
      }

      var group = new THREE.Group()

      for (var i = 0, il = meshes.length; i < il; i++) {
        group.add(meshes[i])
      }

      return group
    })
  }

  /**
   * Specification: https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#cameras
   * @param {number} cameraIndex
   * @return {Promise<THREE.Camera>}
   */
  GLTFParser.prototype.loadCamera = function(cameraIndex) {
    var camera
    var cameraDef = this.json.cameras[cameraIndex]
    var params = cameraDef[cameraDef.type]

    if (!params) {
      console.warn('THREE.GLTFLoader: Missing camera parameters.')
      return
    }

    if (cameraDef.type === 'perspective') {
      camera = new THREE.PerspectiveCamera(THREE.MathUtils.radToDeg(params.yfov), params.aspectRatio || 1, params.znear || 1, params.zfar || 2e6)
    } else if (cameraDef.type === 'orthographic') {
      camera = new THREE.OrthographicCamera(-params.xmag, params.xmag, params.ymag, -params.ymag, params.znear, params.zfar)
    }

    if (cameraDef.name) camera.name = this.createUniqueName(cameraDef.name)

    assignExtrasToUserData(camera, cameraDef)

    return Promise.resolve(camera)
  }

  /**
   * Specification: https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#skins
   * @param {number} skinIndex
   * @return {Promise<Object>}
   */
  GLTFParser.prototype.loadSkin = function(skinIndex) {
    var skinDef = this.json.skins[skinIndex]

    var skinEntry = { joints: skinDef.joints }

    if (skinDef.inverseBindMatrices === undefined) {
      return Promise.resolve(skinEntry)
    }

    return this.getDependency('accessor', skinDef.inverseBindMatrices).then(function(accessor) {
      skinEntry.inverseBindMatrices = accessor

      return skinEntry
    })
  }

  /**
   * Specification: https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#animations
   * @param {number} animationIndex
   * @return {Promise<THREE.AnimationClip>}
   */
  GLTFParser.prototype.loadAnimation = function(animationIndex) {
    var json = this.json

    var animationDef = json.animations[animationIndex]

    var pendingNodes = []
    var pendingInputAccessors = []
    var pendingOutputAccessors = []
    var pendingSamplers = []
    var pendingTargets = []

    for (var i = 0, il = animationDef.channels.length; i < il; i++) {
      var channel = animationDef.channels[i]
      var sampler = animationDef.samplers[channel.sampler]
      var target = channel.target
      var name = target.node !== undefined ? target.node : target.id // NOTE: target.id is deprecated.
      var input = animationDef.parameters !== undefined ? animationDef.parameters[sampler.input] : sampler.input
      var output = animationDef.parameters !== undefined ? animationDef.parameters[sampler.output] : sampler.output

      pendingNodes.push(this.getDependency('node', name))
      pendingInputAccessors.push(this.getDependency('accessor', input))
      pendingOutputAccessors.push(this.getDependency('accessor', output))
      pendingSamplers.push(sampler)
      pendingTargets.push(target)
    }

    return Promise.all([
      Promise.all(pendingNodes),
      Promise.all(pendingInputAccessors),
      Promise.all(pendingOutputAccessors),
      Promise.all(pendingSamplers),
      Promise.all(pendingTargets)
    ]).then(function(dependencies) {
      var nodes = dependencies[0]
      var inputAccessors = dependencies[1]
      var outputAccessors = dependencies[2]
      var samplers = dependencies[3]
      var targets = dependencies[4]

      var tracks = []

      for (var i = 0, il = nodes.length; i < il; i++) {
        var node = nodes[i]
        var inputAccessor = inputAccessors[i]
        var outputAccessor = outputAccessors[i]
        var sampler = samplers[i]
        var target = targets[i]

        if (node === undefined) continue

        node.updateMatrix()
        node.matrixAutoUpdate = true

        var TypedKeyframeTrack

        switch (PATH_PROPERTIES[target.path]) {
          case PATH_PROPERTIES.weights:
            TypedKeyframeTrack = THREE.NumberKeyframeTrack
            break

          case PATH_PROPERTIES.rotation:
            TypedKeyframeTrack = THREE.QuaternionKeyframeTrack
            break

          case PATH_PROPERTIES.position:
          case PATH_PROPERTIES.scale:
          default:
            TypedKeyframeTrack = THREE.VectorKeyframeTrack
            break
        }

        var targetName = node.name ? node.name : node.uuid

        var interpolation = sampler.interpolation !== undefined ? INTERPOLATION[sampler.interpolation] : THREE.InterpolateLinear

        var targetNames = []

        if (PATH_PROPERTIES[target.path] === PATH_PROPERTIES.weights) {
          // Node may be a THREE.Group (glTF mesh with several primitives) or a THREE.Mesh.
          node.traverse(function(object) {
            if (object.isMesh === true && object.morphTargetInfluences) {
              targetNames.push(object.name ? object.name : object.uuid)
            }
          })
        } else {
          targetNames.push(targetName)
        }

        var outputArray = outputAccessor.array

        if (outputAccessor.normalized) {
          var scale

          if (outputArray.constructor === Int8Array) {
            scale = 1 / 127
          } else if (outputArray.constructor === Uint8Array) {
            scale = 1 / 255
          } else if (outputArray.constructor == Int16Array) {
            scale = 1 / 32767
          } else if (outputArray.constructor === Uint16Array) {
            scale = 1 / 65535
          } else {
            throw new Error('THREE.GLTFLoader: Unsupported output accessor component type.')
          }

          var scaled = new Float32Array(outputArray.length)

          for (var j = 0, jl = outputArray.length; j < jl; j++) {
            scaled[j] = outputArray[j] * scale
          }

          outputArray = scaled
        }

        for (var j = 0, jl = targetNames.length; j < jl; j++) {
          var track = new TypedKeyframeTrack(targetNames[j] + '.' + PATH_PROPERTIES[target.path], inputAccessor.array, outputArray, interpolation)

          // Override interpolation with custom factory method.
          if (sampler.interpolation === 'CUBICSPLINE') {
            track.createInterpolant = function InterpolantFactoryMethodGLTFCubicSpline(result) {
              // A CUBICSPLINE keyframe in glTF has three output values for each input value,
              // representing inTangent, splineVertex, and outTangent. As a result, track.getValueSize()
              // must be divided by three to get the interpolant's sampleSize argument.

              return new GLTFCubicSplineInterpolant(this.times, this.values, this.getValueSize() / 3, result)
            }

            // Mark as CUBICSPLINE. `track.getInterpolation()` doesn't support custom interpolants.
            track.createInterpolant.isInterpolantFactoryMethodGLTFCubicSpline = true
          }

          tracks.push(track)
        }
      }

      var name = animationDef.name ? animationDef.name : 'animation_' + animationIndex

      return new THREE.AnimationClip(name, undefined, tracks)
    })
  }

  /**
   * Specification: https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#nodes-and-hierarchy
   * @param {number} nodeIndex
   * @return {Promise<THREE.Object3D>}
   */
  GLTFParser.prototype.loadNode = function(nodeIndex) {
    var json = this.json
    var extensions = this.extensions
    var parser = this

    var nodeDef = json.nodes[nodeIndex]

    // reserve node's name before its dependencies, so the root has the intended name.
    var nodeName = nodeDef.name ? parser.createUniqueName(nodeDef.name) : ''

    return (function() {
      var pending = []

      if (nodeDef.mesh !== undefined) {
        pending.push(
          parser.getDependency('mesh', nodeDef.mesh).then(function(mesh) {
            var node = parser._getNodeRef(parser.meshCache, nodeDef.mesh, mesh)

            // if weights are provided on the node, override weights on the mesh.
            if (nodeDef.weights !== undefined) {
              node.traverse(function(o) {
                if (!o.isMesh) return

                for (var i = 0, il = nodeDef.weights.length; i < il; i++) {
                  o.morphTargetInfluences[i] = nodeDef.weights[i]
                }
              })
            }

            return node
          })
        )
      }

      if (nodeDef.camera !== undefined) {
        pending.push(
          parser.getDependency('camera', nodeDef.camera).then(function(camera) {
            return parser._getNodeRef(parser.cameraCache, nodeDef.camera, camera)
          })
        )
      }

      parser
        ._invokeAll(function(ext) {
          return ext.createNodeAttachment && ext.createNodeAttachment(nodeIndex)
        })
        .forEach(function(promise) {
          pending.push(promise)
        })

      return Promise.all(pending)
    })().then(function(objects) {
      var node

      // .isBone isn't in glTF spec. See ._markDefs
      if (nodeDef.isBone === true) {
        node = new THREE.Bone()
      } else if (objects.length > 1) {
        node = new THREE.Group()
      } else if (objects.length === 1) {
        node = objects[0]
      } else {
        node = new THREE.Object3D()
      }

      if (node !== objects[0]) {
        for (var i = 0, il = objects.length; i < il; i++) {
          node.add(objects[i])
        }
      }

      if (nodeDef.name) {
        node.userData.name = nodeDef.name
        node.name = nodeName
      }

      assignExtrasToUserData(node, nodeDef)

      if (nodeDef.extensions) addUnknownExtensionsToUserData(extensions, node, nodeDef)

      if (nodeDef.matrix !== undefined) {
        var matrix = new THREE.Matrix4()
        matrix.fromArray(nodeDef.matrix)
        node.applyMatrix4(matrix)
      } else {
        if (nodeDef.translation !== undefined) {
          node.position.fromArray(nodeDef.translation)
        }

        if (nodeDef.rotation !== undefined) {
          node.quaternion.fromArray(nodeDef.rotation)
        }

        if (nodeDef.scale !== undefined) {
          node.scale.fromArray(nodeDef.scale)
        }
      }

      parser.associations.set(node, { type: 'nodes', index: nodeIndex })

      return node
    })
  }

  /**
   * Specification: https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#scenes
   * @param {number} sceneIndex
   * @return {Promise<THREE.Group>}
   */
  GLTFParser.prototype.loadScene = (function() {
    // scene node hierachy builder

    function buildNodeHierachy(nodeId, parentObject, json, parser) {
      var nodeDef = json.nodes[nodeId]

      return parser
        .getDependency('node', nodeId)
        .then(function(node) {
          if (nodeDef.skin === undefined) return node

          // build skeleton here as well

          var skinEntry

          return parser
            .getDependency('skin', nodeDef.skin)
            .then(function(skin) {
              skinEntry = skin

              var pendingJoints = []

              for (var i = 0, il = skinEntry.joints.length; i < il; i++) {
                pendingJoints.push(parser.getDependency('node', skinEntry.joints[i]))
              }

              return Promise.all(pendingJoints)
            })
            .then(function(jointNodes) {
              node.traverse(function(mesh) {
                if (!mesh.isMesh) return

                var bones = []
                var boneInverses = []

                for (var j = 0, jl = jointNodes.length; j < jl; j++) {
                  var jointNode = jointNodes[j]

                  if (jointNode) {
                    bones.push(jointNode)

                    var mat = new THREE.Matrix4()

                    if (skinEntry.inverseBindMatrices !== undefined) {
                      mat.fromArray(skinEntry.inverseBindMatrices.array, j * 16)
                    }

                    boneInverses.push(mat)
                  } else {
                    console.warn('THREE.GLTFLoader: Joint "%s" could not be found.', skinEntry.joints[j])
                  }
                }

                mesh.bind(new THREE.Skeleton(bones, boneInverses), mesh.matrixWorld)
              })

              return node
            })
        })
        .then(function(node) {
          // build node hierachy

          parentObject.add(node)

          var pending = []

          if (nodeDef.children) {
            var children = nodeDef.children

            for (var i = 0, il = children.length; i < il; i++) {
              var child = children[i]
              pending.push(buildNodeHierachy(child, node, json, parser))
            }
          }

          return Promise.all(pending)
        })
    }

    return function loadScene(sceneIndex) {
      var json = this.json
      var extensions = this.extensions
      var sceneDef = this.json.scenes[sceneIndex]
      var parser = this

      // Loader returns Group, not Scene.
      // See: https://github.com/mrdoob/three.js/issues/18342#issuecomment-578981172
      var scene = new THREE.Group()
      if (sceneDef.name) scene.name = parser.createUniqueName(sceneDef.name)

      assignExtrasToUserData(scene, sceneDef)

      if (sceneDef.extensions) addUnknownExtensionsToUserData(extensions, scene, sceneDef)

      var nodeIds = sceneDef.nodes || []

      var pending = []

      for (var i = 0, il = nodeIds.length; i < il; i++) {
        pending.push(buildNodeHierachy(nodeIds[i], scene, json, parser))
      }

      return Promise.all(pending).then(function() {
        return scene
      })
    }
  })()

  return GLTFLoader
})()
